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TOMOYO Linux Cross Reference
Linux/fs/kernfs/file.c

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  1 /*
  2  * fs/kernfs/file.c - kernfs file implementation
  3  *
  4  * Copyright (c) 2001-3 Patrick Mochel
  5  * Copyright (c) 2007 SUSE Linux Products GmbH
  6  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
  7  *
  8  * This file is released under the GPLv2.
  9  */
 10 
 11 #include <linux/fs.h>
 12 #include <linux/seq_file.h>
 13 #include <linux/slab.h>
 14 #include <linux/poll.h>
 15 #include <linux/pagemap.h>
 16 #include <linux/sched.h>
 17 
 18 #include "kernfs-internal.h"
 19 
 20 /*
 21  * There's one kernfs_open_file for each open file and one kernfs_open_node
 22  * for each kernfs_node with one or more open files.
 23  *
 24  * kernfs_node->attr.open points to kernfs_open_node.  attr.open is
 25  * protected by kernfs_open_node_lock.
 26  *
 27  * filp->private_data points to seq_file whose ->private points to
 28  * kernfs_open_file.  kernfs_open_files are chained at
 29  * kernfs_open_node->files, which is protected by kernfs_open_file_mutex.
 30  */
 31 static DEFINE_SPINLOCK(kernfs_open_node_lock);
 32 static DEFINE_MUTEX(kernfs_open_file_mutex);
 33 
 34 struct kernfs_open_node {
 35         atomic_t                refcnt;
 36         atomic_t                event;
 37         wait_queue_head_t       poll;
 38         struct list_head        files; /* goes through kernfs_open_file.list */
 39 };
 40 
 41 static struct kernfs_open_file *kernfs_of(struct file *file)
 42 {
 43         return ((struct seq_file *)file->private_data)->private;
 44 }
 45 
 46 /*
 47  * Determine the kernfs_ops for the given kernfs_node.  This function must
 48  * be called while holding an active reference.
 49  */
 50 static const struct kernfs_ops *kernfs_ops(struct kernfs_node *kn)
 51 {
 52         if (kn->flags & KERNFS_LOCKDEP)
 53                 lockdep_assert_held(kn);
 54         return kn->attr.ops;
 55 }
 56 
 57 /*
 58  * As kernfs_seq_stop() is also called after kernfs_seq_start() or
 59  * kernfs_seq_next() failure, it needs to distinguish whether it's stopping
 60  * a seq_file iteration which is fully initialized with an active reference
 61  * or an aborted kernfs_seq_start() due to get_active failure.  The
 62  * position pointer is the only context for each seq_file iteration and
 63  * thus the stop condition should be encoded in it.  As the return value is
 64  * directly visible to userland, ERR_PTR(-ENODEV) is the only acceptable
 65  * choice to indicate get_active failure.
 66  *
 67  * Unfortunately, this is complicated due to the optional custom seq_file
 68  * operations which may return ERR_PTR(-ENODEV) too.  kernfs_seq_stop()
 69  * can't distinguish whether ERR_PTR(-ENODEV) is from get_active failure or
 70  * custom seq_file operations and thus can't decide whether put_active
 71  * should be performed or not only on ERR_PTR(-ENODEV).
 72  *
 73  * This is worked around by factoring out the custom seq_stop() and
 74  * put_active part into kernfs_seq_stop_active(), skipping it from
 75  * kernfs_seq_stop() if ERR_PTR(-ENODEV) while invoking it directly after
 76  * custom seq_file operations fail with ERR_PTR(-ENODEV) - this ensures
 77  * that kernfs_seq_stop_active() is skipped only after get_active failure.
 78  */
 79 static void kernfs_seq_stop_active(struct seq_file *sf, void *v)
 80 {
 81         struct kernfs_open_file *of = sf->private;
 82         const struct kernfs_ops *ops = kernfs_ops(of->kn);
 83 
 84         if (ops->seq_stop)
 85                 ops->seq_stop(sf, v);
 86         kernfs_put_active(of->kn);
 87 }
 88 
 89 static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
 90 {
 91         struct kernfs_open_file *of = sf->private;
 92         const struct kernfs_ops *ops;
 93 
 94         /*
 95          * @of->mutex nests outside active ref and is just to ensure that
 96          * the ops aren't called concurrently for the same open file.
 97          */
 98         mutex_lock(&of->mutex);
 99         if (!kernfs_get_active(of->kn))
100                 return ERR_PTR(-ENODEV);
101 
102         ops = kernfs_ops(of->kn);
103         if (ops->seq_start) {
104                 void *next = ops->seq_start(sf, ppos);
105                 /* see the comment above kernfs_seq_stop_active() */
106                 if (next == ERR_PTR(-ENODEV))
107                         kernfs_seq_stop_active(sf, next);
108                 return next;
109         } else {
110                 /*
111                  * The same behavior and code as single_open().  Returns
112                  * !NULL if pos is at the beginning; otherwise, NULL.
113                  */
114                 return NULL + !*ppos;
115         }
116 }
117 
118 static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)
119 {
120         struct kernfs_open_file *of = sf->private;
121         const struct kernfs_ops *ops = kernfs_ops(of->kn);
122 
123         if (ops->seq_next) {
124                 void *next = ops->seq_next(sf, v, ppos);
125                 /* see the comment above kernfs_seq_stop_active() */
126                 if (next == ERR_PTR(-ENODEV))
127                         kernfs_seq_stop_active(sf, next);
128                 return next;
129         } else {
130                 /*
131                  * The same behavior and code as single_open(), always
132                  * terminate after the initial read.
133                  */
134                 ++*ppos;
135                 return NULL;
136         }
137 }
138 
139 static void kernfs_seq_stop(struct seq_file *sf, void *v)
140 {
141         struct kernfs_open_file *of = sf->private;
142 
143         if (v != ERR_PTR(-ENODEV))
144                 kernfs_seq_stop_active(sf, v);
145         mutex_unlock(&of->mutex);
146 }
147 
148 static int kernfs_seq_show(struct seq_file *sf, void *v)
149 {
150         struct kernfs_open_file *of = sf->private;
151 
152         of->event = atomic_read(&of->kn->attr.open->event);
153 
154         return of->kn->attr.ops->seq_show(sf, v);
155 }
156 
157 static const struct seq_operations kernfs_seq_ops = {
158         .start = kernfs_seq_start,
159         .next = kernfs_seq_next,
160         .stop = kernfs_seq_stop,
161         .show = kernfs_seq_show,
162 };
163 
164 /*
165  * As reading a bin file can have side-effects, the exact offset and bytes
166  * specified in read(2) call should be passed to the read callback making
167  * it difficult to use seq_file.  Implement simplistic custom buffering for
168  * bin files.
169  */
170 static ssize_t kernfs_file_direct_read(struct kernfs_open_file *of,
171                                        char __user *user_buf, size_t count,
172                                        loff_t *ppos)
173 {
174         ssize_t len = min_t(size_t, count, PAGE_SIZE);
175         const struct kernfs_ops *ops;
176         char *buf;
177 
178         buf = kmalloc(len, GFP_KERNEL);
179         if (!buf)
180                 return -ENOMEM;
181 
182         /*
183          * @of->mutex nests outside active ref and is just to ensure that
184          * the ops aren't called concurrently for the same open file.
185          */
186         mutex_lock(&of->mutex);
187         if (!kernfs_get_active(of->kn)) {
188                 len = -ENODEV;
189                 mutex_unlock(&of->mutex);
190                 goto out_free;
191         }
192 
193         ops = kernfs_ops(of->kn);
194         if (ops->read)
195                 len = ops->read(of, buf, len, *ppos);
196         else
197                 len = -EINVAL;
198 
199         kernfs_put_active(of->kn);
200         mutex_unlock(&of->mutex);
201 
202         if (len < 0)
203                 goto out_free;
204 
205         if (copy_to_user(user_buf, buf, len)) {
206                 len = -EFAULT;
207                 goto out_free;
208         }
209 
210         *ppos += len;
211 
212  out_free:
213         kfree(buf);
214         return len;
215 }
216 
217 /**
218  * kernfs_fop_read - kernfs vfs read callback
219  * @file: file pointer
220  * @user_buf: data to write
221  * @count: number of bytes
222  * @ppos: starting offset
223  */
224 static ssize_t kernfs_fop_read(struct file *file, char __user *user_buf,
225                                size_t count, loff_t *ppos)
226 {
227         struct kernfs_open_file *of = kernfs_of(file);
228 
229         if (of->kn->flags & KERNFS_HAS_SEQ_SHOW)
230                 return seq_read(file, user_buf, count, ppos);
231         else
232                 return kernfs_file_direct_read(of, user_buf, count, ppos);
233 }
234 
235 /**
236  * kernfs_fop_write - kernfs vfs write callback
237  * @file: file pointer
238  * @user_buf: data to write
239  * @count: number of bytes
240  * @ppos: starting offset
241  *
242  * Copy data in from userland and pass it to the matching kernfs write
243  * operation.
244  *
245  * There is no easy way for us to know if userspace is only doing a partial
246  * write, so we don't support them. We expect the entire buffer to come on
247  * the first write.  Hint: if you're writing a value, first read the file,
248  * modify only the the value you're changing, then write entire buffer
249  * back.
250  */
251 static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
252                                 size_t count, loff_t *ppos)
253 {
254         struct kernfs_open_file *of = kernfs_of(file);
255         const struct kernfs_ops *ops;
256         size_t len;
257         char *buf;
258 
259         if (of->atomic_write_len) {
260                 len = count;
261                 if (len > of->atomic_write_len)
262                         return -E2BIG;
263         } else {
264                 len = min_t(size_t, count, PAGE_SIZE);
265         }
266 
267         buf = kmalloc(len + 1, GFP_KERNEL);
268         if (!buf)
269                 return -ENOMEM;
270 
271         if (copy_from_user(buf, user_buf, len)) {
272                 len = -EFAULT;
273                 goto out_free;
274         }
275         buf[len] = '\0';        /* guarantee string termination */
276 
277         /*
278          * @of->mutex nests outside active ref and is just to ensure that
279          * the ops aren't called concurrently for the same open file.
280          */
281         mutex_lock(&of->mutex);
282         if (!kernfs_get_active(of->kn)) {
283                 mutex_unlock(&of->mutex);
284                 len = -ENODEV;
285                 goto out_free;
286         }
287 
288         ops = kernfs_ops(of->kn);
289         if (ops->write)
290                 len = ops->write(of, buf, len, *ppos);
291         else
292                 len = -EINVAL;
293 
294         kernfs_put_active(of->kn);
295         mutex_unlock(&of->mutex);
296 
297         if (len > 0)
298                 *ppos += len;
299 out_free:
300         kfree(buf);
301         return len;
302 }
303 
304 static void kernfs_vma_open(struct vm_area_struct *vma)
305 {
306         struct file *file = vma->vm_file;
307         struct kernfs_open_file *of = kernfs_of(file);
308 
309         if (!of->vm_ops)
310                 return;
311 
312         if (!kernfs_get_active(of->kn))
313                 return;
314 
315         if (of->vm_ops->open)
316                 of->vm_ops->open(vma);
317 
318         kernfs_put_active(of->kn);
319 }
320 
321 static int kernfs_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
322 {
323         struct file *file = vma->vm_file;
324         struct kernfs_open_file *of = kernfs_of(file);
325         int ret;
326 
327         if (!of->vm_ops)
328                 return VM_FAULT_SIGBUS;
329 
330         if (!kernfs_get_active(of->kn))
331                 return VM_FAULT_SIGBUS;
332 
333         ret = VM_FAULT_SIGBUS;
334         if (of->vm_ops->fault)
335                 ret = of->vm_ops->fault(vma, vmf);
336 
337         kernfs_put_active(of->kn);
338         return ret;
339 }
340 
341 static int kernfs_vma_page_mkwrite(struct vm_area_struct *vma,
342                                    struct vm_fault *vmf)
343 {
344         struct file *file = vma->vm_file;
345         struct kernfs_open_file *of = kernfs_of(file);
346         int ret;
347 
348         if (!of->vm_ops)
349                 return VM_FAULT_SIGBUS;
350 
351         if (!kernfs_get_active(of->kn))
352                 return VM_FAULT_SIGBUS;
353 
354         ret = 0;
355         if (of->vm_ops->page_mkwrite)
356                 ret = of->vm_ops->page_mkwrite(vma, vmf);
357         else
358                 file_update_time(file);
359 
360         kernfs_put_active(of->kn);
361         return ret;
362 }
363 
364 static int kernfs_vma_access(struct vm_area_struct *vma, unsigned long addr,
365                              void *buf, int len, int write)
366 {
367         struct file *file = vma->vm_file;
368         struct kernfs_open_file *of = kernfs_of(file);
369         int ret;
370 
371         if (!of->vm_ops)
372                 return -EINVAL;
373 
374         if (!kernfs_get_active(of->kn))
375                 return -EINVAL;
376 
377         ret = -EINVAL;
378         if (of->vm_ops->access)
379                 ret = of->vm_ops->access(vma, addr, buf, len, write);
380 
381         kernfs_put_active(of->kn);
382         return ret;
383 }
384 
385 #ifdef CONFIG_NUMA
386 static int kernfs_vma_set_policy(struct vm_area_struct *vma,
387                                  struct mempolicy *new)
388 {
389         struct file *file = vma->vm_file;
390         struct kernfs_open_file *of = kernfs_of(file);
391         int ret;
392 
393         if (!of->vm_ops)
394                 return 0;
395 
396         if (!kernfs_get_active(of->kn))
397                 return -EINVAL;
398 
399         ret = 0;
400         if (of->vm_ops->set_policy)
401                 ret = of->vm_ops->set_policy(vma, new);
402 
403         kernfs_put_active(of->kn);
404         return ret;
405 }
406 
407 static struct mempolicy *kernfs_vma_get_policy(struct vm_area_struct *vma,
408                                                unsigned long addr)
409 {
410         struct file *file = vma->vm_file;
411         struct kernfs_open_file *of = kernfs_of(file);
412         struct mempolicy *pol;
413 
414         if (!of->vm_ops)
415                 return vma->vm_policy;
416 
417         if (!kernfs_get_active(of->kn))
418                 return vma->vm_policy;
419 
420         pol = vma->vm_policy;
421         if (of->vm_ops->get_policy)
422                 pol = of->vm_ops->get_policy(vma, addr);
423 
424         kernfs_put_active(of->kn);
425         return pol;
426 }
427 
428 static int kernfs_vma_migrate(struct vm_area_struct *vma,
429                               const nodemask_t *from, const nodemask_t *to,
430                               unsigned long flags)
431 {
432         struct file *file = vma->vm_file;
433         struct kernfs_open_file *of = kernfs_of(file);
434         int ret;
435 
436         if (!of->vm_ops)
437                 return 0;
438 
439         if (!kernfs_get_active(of->kn))
440                 return 0;
441 
442         ret = 0;
443         if (of->vm_ops->migrate)
444                 ret = of->vm_ops->migrate(vma, from, to, flags);
445 
446         kernfs_put_active(of->kn);
447         return ret;
448 }
449 #endif
450 
451 static const struct vm_operations_struct kernfs_vm_ops = {
452         .open           = kernfs_vma_open,
453         .fault          = kernfs_vma_fault,
454         .page_mkwrite   = kernfs_vma_page_mkwrite,
455         .access         = kernfs_vma_access,
456 #ifdef CONFIG_NUMA
457         .set_policy     = kernfs_vma_set_policy,
458         .get_policy     = kernfs_vma_get_policy,
459         .migrate        = kernfs_vma_migrate,
460 #endif
461 };
462 
463 static int kernfs_fop_mmap(struct file *file, struct vm_area_struct *vma)
464 {
465         struct kernfs_open_file *of = kernfs_of(file);
466         const struct kernfs_ops *ops;
467         int rc;
468 
469         /*
470          * mmap path and of->mutex are prone to triggering spurious lockdep
471          * warnings and we don't want to add spurious locking dependency
472          * between the two.  Check whether mmap is actually implemented
473          * without grabbing @of->mutex by testing HAS_MMAP flag.  See the
474          * comment in kernfs_file_open() for more details.
475          */
476         if (!(of->kn->flags & KERNFS_HAS_MMAP))
477                 return -ENODEV;
478 
479         mutex_lock(&of->mutex);
480 
481         rc = -ENODEV;
482         if (!kernfs_get_active(of->kn))
483                 goto out_unlock;
484 
485         ops = kernfs_ops(of->kn);
486         rc = ops->mmap(of, vma);
487         if (rc)
488                 goto out_put;
489 
490         /*
491          * PowerPC's pci_mmap of legacy_mem uses shmem_zero_setup()
492          * to satisfy versions of X which crash if the mmap fails: that
493          * substitutes a new vm_file, and we don't then want bin_vm_ops.
494          */
495         if (vma->vm_file != file)
496                 goto out_put;
497 
498         rc = -EINVAL;
499         if (of->mmapped && of->vm_ops != vma->vm_ops)
500                 goto out_put;
501 
502         /*
503          * It is not possible to successfully wrap close.
504          * So error if someone is trying to use close.
505          */
506         rc = -EINVAL;
507         if (vma->vm_ops && vma->vm_ops->close)
508                 goto out_put;
509 
510         rc = 0;
511         of->mmapped = 1;
512         of->vm_ops = vma->vm_ops;
513         vma->vm_ops = &kernfs_vm_ops;
514 out_put:
515         kernfs_put_active(of->kn);
516 out_unlock:
517         mutex_unlock(&of->mutex);
518 
519         return rc;
520 }
521 
522 /**
523  *      kernfs_get_open_node - get or create kernfs_open_node
524  *      @kn: target kernfs_node
525  *      @of: kernfs_open_file for this instance of open
526  *
527  *      If @kn->attr.open exists, increment its reference count; otherwise,
528  *      create one.  @of is chained to the files list.
529  *
530  *      LOCKING:
531  *      Kernel thread context (may sleep).
532  *
533  *      RETURNS:
534  *      0 on success, -errno on failure.
535  */
536 static int kernfs_get_open_node(struct kernfs_node *kn,
537                                 struct kernfs_open_file *of)
538 {
539         struct kernfs_open_node *on, *new_on = NULL;
540 
541  retry:
542         mutex_lock(&kernfs_open_file_mutex);
543         spin_lock_irq(&kernfs_open_node_lock);
544 
545         if (!kn->attr.open && new_on) {
546                 kn->attr.open = new_on;
547                 new_on = NULL;
548         }
549 
550         on = kn->attr.open;
551         if (on) {
552                 atomic_inc(&on->refcnt);
553                 list_add_tail(&of->list, &on->files);
554         }
555 
556         spin_unlock_irq(&kernfs_open_node_lock);
557         mutex_unlock(&kernfs_open_file_mutex);
558 
559         if (on) {
560                 kfree(new_on);
561                 return 0;
562         }
563 
564         /* not there, initialize a new one and retry */
565         new_on = kmalloc(sizeof(*new_on), GFP_KERNEL);
566         if (!new_on)
567                 return -ENOMEM;
568 
569         atomic_set(&new_on->refcnt, 0);
570         atomic_set(&new_on->event, 1);
571         init_waitqueue_head(&new_on->poll);
572         INIT_LIST_HEAD(&new_on->files);
573         goto retry;
574 }
575 
576 /**
577  *      kernfs_put_open_node - put kernfs_open_node
578  *      @kn: target kernfs_nodet
579  *      @of: associated kernfs_open_file
580  *
581  *      Put @kn->attr.open and unlink @of from the files list.  If
582  *      reference count reaches zero, disassociate and free it.
583  *
584  *      LOCKING:
585  *      None.
586  */
587 static void kernfs_put_open_node(struct kernfs_node *kn,
588                                  struct kernfs_open_file *of)
589 {
590         struct kernfs_open_node *on = kn->attr.open;
591         unsigned long flags;
592 
593         mutex_lock(&kernfs_open_file_mutex);
594         spin_lock_irqsave(&kernfs_open_node_lock, flags);
595 
596         if (of)
597                 list_del(&of->list);
598 
599         if (atomic_dec_and_test(&on->refcnt))
600                 kn->attr.open = NULL;
601         else
602                 on = NULL;
603 
604         spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
605         mutex_unlock(&kernfs_open_file_mutex);
606 
607         kfree(on);
608 }
609 
610 static int kernfs_fop_open(struct inode *inode, struct file *file)
611 {
612         struct kernfs_node *kn = file->f_path.dentry->d_fsdata;
613         struct kernfs_root *root = kernfs_root(kn);
614         const struct kernfs_ops *ops;
615         struct kernfs_open_file *of;
616         bool has_read, has_write, has_mmap;
617         int error = -EACCES;
618 
619         if (!kernfs_get_active(kn))
620                 return -ENODEV;
621 
622         ops = kernfs_ops(kn);
623 
624         has_read = ops->seq_show || ops->read || ops->mmap;
625         has_write = ops->write || ops->mmap;
626         has_mmap = ops->mmap;
627 
628         /* see the flag definition for details */
629         if (root->flags & KERNFS_ROOT_EXTRA_OPEN_PERM_CHECK) {
630                 if ((file->f_mode & FMODE_WRITE) &&
631                     (!(inode->i_mode & S_IWUGO) || !has_write))
632                         goto err_out;
633 
634                 if ((file->f_mode & FMODE_READ) &&
635                     (!(inode->i_mode & S_IRUGO) || !has_read))
636                         goto err_out;
637         }
638 
639         /* allocate a kernfs_open_file for the file */
640         error = -ENOMEM;
641         of = kzalloc(sizeof(struct kernfs_open_file), GFP_KERNEL);
642         if (!of)
643                 goto err_out;
644 
645         /*
646          * The following is done to give a different lockdep key to
647          * @of->mutex for files which implement mmap.  This is a rather
648          * crude way to avoid false positive lockdep warning around
649          * mm->mmap_sem - mmap nests @of->mutex under mm->mmap_sem and
650          * reading /sys/block/sda/trace/act_mask grabs sr_mutex, under
651          * which mm->mmap_sem nests, while holding @of->mutex.  As each
652          * open file has a separate mutex, it's okay as long as those don't
653          * happen on the same file.  At this point, we can't easily give
654          * each file a separate locking class.  Let's differentiate on
655          * whether the file has mmap or not for now.
656          *
657          * Both paths of the branch look the same.  They're supposed to
658          * look that way and give @of->mutex different static lockdep keys.
659          */
660         if (has_mmap)
661                 mutex_init(&of->mutex);
662         else
663                 mutex_init(&of->mutex);
664 
665         of->kn = kn;
666         of->file = file;
667 
668         /*
669          * Write path needs to atomic_write_len outside active reference.
670          * Cache it in open_file.  See kernfs_fop_write() for details.
671          */
672         of->atomic_write_len = ops->atomic_write_len;
673 
674         /*
675          * Always instantiate seq_file even if read access doesn't use
676          * seq_file or is not requested.  This unifies private data access
677          * and readable regular files are the vast majority anyway.
678          */
679         if (ops->seq_show)
680                 error = seq_open(file, &kernfs_seq_ops);
681         else
682                 error = seq_open(file, NULL);
683         if (error)
684                 goto err_free;
685 
686         ((struct seq_file *)file->private_data)->private = of;
687 
688         /* seq_file clears PWRITE unconditionally, restore it if WRITE */
689         if (file->f_mode & FMODE_WRITE)
690                 file->f_mode |= FMODE_PWRITE;
691 
692         /* make sure we have open node struct */
693         error = kernfs_get_open_node(kn, of);
694         if (error)
695                 goto err_close;
696 
697         /* open succeeded, put active references */
698         kernfs_put_active(kn);
699         return 0;
700 
701 err_close:
702         seq_release(inode, file);
703 err_free:
704         kfree(of);
705 err_out:
706         kernfs_put_active(kn);
707         return error;
708 }
709 
710 static int kernfs_fop_release(struct inode *inode, struct file *filp)
711 {
712         struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
713         struct kernfs_open_file *of = kernfs_of(filp);
714 
715         kernfs_put_open_node(kn, of);
716         seq_release(inode, filp);
717         kfree(of);
718 
719         return 0;
720 }
721 
722 void kernfs_unmap_bin_file(struct kernfs_node *kn)
723 {
724         struct kernfs_open_node *on;
725         struct kernfs_open_file *of;
726 
727         if (!(kn->flags & KERNFS_HAS_MMAP))
728                 return;
729 
730         spin_lock_irq(&kernfs_open_node_lock);
731         on = kn->attr.open;
732         if (on)
733                 atomic_inc(&on->refcnt);
734         spin_unlock_irq(&kernfs_open_node_lock);
735         if (!on)
736                 return;
737 
738         mutex_lock(&kernfs_open_file_mutex);
739         list_for_each_entry(of, &on->files, list) {
740                 struct inode *inode = file_inode(of->file);
741                 unmap_mapping_range(inode->i_mapping, 0, 0, 1);
742         }
743         mutex_unlock(&kernfs_open_file_mutex);
744 
745         kernfs_put_open_node(kn, NULL);
746 }
747 
748 /*
749  * Kernfs attribute files are pollable.  The idea is that you read
750  * the content and then you use 'poll' or 'select' to wait for
751  * the content to change.  When the content changes (assuming the
752  * manager for the kobject supports notification), poll will
753  * return POLLERR|POLLPRI, and select will return the fd whether
754  * it is waiting for read, write, or exceptions.
755  * Once poll/select indicates that the value has changed, you
756  * need to close and re-open the file, or seek to 0 and read again.
757  * Reminder: this only works for attributes which actively support
758  * it, and it is not possible to test an attribute from userspace
759  * to see if it supports poll (Neither 'poll' nor 'select' return
760  * an appropriate error code).  When in doubt, set a suitable timeout value.
761  */
762 static unsigned int kernfs_fop_poll(struct file *filp, poll_table *wait)
763 {
764         struct kernfs_open_file *of = kernfs_of(filp);
765         struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
766         struct kernfs_open_node *on = kn->attr.open;
767 
768         /* need parent for the kobj, grab both */
769         if (!kernfs_get_active(kn))
770                 goto trigger;
771 
772         poll_wait(filp, &on->poll, wait);
773 
774         kernfs_put_active(kn);
775 
776         if (of->event != atomic_read(&on->event))
777                 goto trigger;
778 
779         return DEFAULT_POLLMASK;
780 
781  trigger:
782         return DEFAULT_POLLMASK|POLLERR|POLLPRI;
783 }
784 
785 /**
786  * kernfs_notify - notify a kernfs file
787  * @kn: file to notify
788  *
789  * Notify @kn such that poll(2) on @kn wakes up.
790  */
791 void kernfs_notify(struct kernfs_node *kn)
792 {
793         struct kernfs_open_node *on;
794         unsigned long flags;
795 
796         spin_lock_irqsave(&kernfs_open_node_lock, flags);
797 
798         if (!WARN_ON(kernfs_type(kn) != KERNFS_FILE)) {
799                 on = kn->attr.open;
800                 if (on) {
801                         atomic_inc(&on->event);
802                         wake_up_interruptible(&on->poll);
803                 }
804         }
805 
806         spin_unlock_irqrestore(&kernfs_open_node_lock, flags);
807 }
808 EXPORT_SYMBOL_GPL(kernfs_notify);
809 
810 const struct file_operations kernfs_file_fops = {
811         .read           = kernfs_fop_read,
812         .write          = kernfs_fop_write,
813         .llseek         = generic_file_llseek,
814         .mmap           = kernfs_fop_mmap,
815         .open           = kernfs_fop_open,
816         .release        = kernfs_fop_release,
817         .poll           = kernfs_fop_poll,
818 };
819 
820 /**
821  * __kernfs_create_file - kernfs internal function to create a file
822  * @parent: directory to create the file in
823  * @name: name of the file
824  * @mode: mode of the file
825  * @size: size of the file
826  * @ops: kernfs operations for the file
827  * @priv: private data for the file
828  * @ns: optional namespace tag of the file
829  * @static_name: don't copy file name
830  * @key: lockdep key for the file's active_ref, %NULL to disable lockdep
831  *
832  * Returns the created node on success, ERR_PTR() value on error.
833  */
834 struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
835                                          const char *name,
836                                          umode_t mode, loff_t size,
837                                          const struct kernfs_ops *ops,
838                                          void *priv, const void *ns,
839                                          bool name_is_static,
840                                          struct lock_class_key *key)
841 {
842         struct kernfs_node *kn;
843         unsigned flags;
844         int rc;
845 
846         flags = KERNFS_FILE;
847         if (name_is_static)
848                 flags |= KERNFS_STATIC_NAME;
849 
850         kn = kernfs_new_node(parent, name, (mode & S_IALLUGO) | S_IFREG, flags);
851         if (!kn)
852                 return ERR_PTR(-ENOMEM);
853 
854         kn->attr.ops = ops;
855         kn->attr.size = size;
856         kn->ns = ns;
857         kn->priv = priv;
858 
859 #ifdef CONFIG_DEBUG_LOCK_ALLOC
860         if (key) {
861                 lockdep_init_map(&kn->dep_map, "s_active", key, 0);
862                 kn->flags |= KERNFS_LOCKDEP;
863         }
864 #endif
865 
866         /*
867          * kn->attr.ops is accesible only while holding active ref.  We
868          * need to know whether some ops are implemented outside active
869          * ref.  Cache their existence in flags.
870          */
871         if (ops->seq_show)
872                 kn->flags |= KERNFS_HAS_SEQ_SHOW;
873         if (ops->mmap)
874                 kn->flags |= KERNFS_HAS_MMAP;
875 
876         rc = kernfs_add_one(kn);
877         if (rc) {
878                 kernfs_put(kn);
879                 return ERR_PTR(rc);
880         }
881         return kn;
882 }
883 

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